Furnace



C. L. IPSEN ET AL Junev 21, 1932.

FURNACE Filed )lay 6. 1931 Otis,

Inventors Carl L.lp5er1,- Albe' .N.'

Their` Attorheg.

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wmmwmfmmmmm Patented June 2l, 1932 UNITED STATES PATENT OFFICE cam. L.IrsnN .um ALBERT' N. Oris, or scrranrzc'aumr,l NEW vom; assIoNons ToGENERAL morale COMPANY, a CORPORATION or New Yom:

remmen Application led Hay 6, 1931. Serial No. 535,412.

Our invention relates to furnaces, more articularly to annealingfurnaces and has or its Object the provision of means whereby apredetermined cooling cycle may be obtained.

In certain heating Operations, especially in the annealing of metals, itis often permissible to cool the char e at a more rapid rate than thenaturalcoolmg rate of the furnace when 1a shut down, particularly afterthe charge has cooled down at the natural rate to a prede` 'terminedtemperature, depending on the material being treated. It is, of course,desirablev to decrease the cooling period to the shortest possible timeconsistent with the requirements of the material, in order to increasethe output of the furnace. Many of the alloy steels are very sensitiveto exposure to air at high. temperature, detrimental de-4 carburizationtaking place under these conditain steels must be cooled at a. fairlyslow rate until they are below a red heat, after which the cooling ratemay be increased although 1t must still be kept lower than would resultfrom removal of the material from the fur' nace. 'The cooling may oftenbe permissible at an increasing rate with the material in the furnacedown to a certain point, depending upon the characteristics of thematerial, when the charge may be removed from the furnace and allowed tocool in the open air.

In carrying out our invention we provide cooling means for the furnacewhereby the desired rates of cooling may be obtained comprising coolingducts in the furnace through which air is forced during one period ofthe cooling cycle, and apertures which may be opened to provide forcirculation of the outside air directly through the furnace duringanother portion of the cooling cycle, after which the charge may beremoved.

For a more complete understanding of our invention reference should behad to the accompanying drawing, Fig. 1 of which is a View partially insection, of an electric furnace embodying ourinvention; Fig. 2 is adiagrammatic view showing details of con struction, while Fig. 3 showscurvesillustratinv typical coolingc cles. 4

tleferringf to the rawing, we have shown our invention in one form inconnection with an electrically,y heated furnace 'although it will beunderstood that various other suitable forms of heat may be used. In theform shown the Ifurnace'c'omprises suitable heat refractory 'walls 1()surrounded by a metallic supporting framework 11. This frameworkl alsocarries suitable means (not shown) for raising and lowering a door 12 atone end of the furnace. The bottom of this furnace on which the chargeis placed on hearth plates 13 is mounted on .wheels 14 which run' ontracks 15 and 16 whereby when the door is lifted the bottom, which is inthe form of-a car, can be run out of the furnaceon the tracks tofacilitate loading and unloading of the charge. As shown, the car may bemoved into and out of the .furnace by means of a stationary gear 17mounted below the car and engaging with a rack 18 carried by the car.The gear may be turned through a shaft 19 and a reduction gearing 20through which connection is made to a suitable elec,- tric drivingmotor, not shown. Suitable electric heating resistors 21 are mounted onheat refractory insulating supports' secured to the wall of the furnace.

To provide. forced cooling-during one portion of the cooling cycle wehave provided a plurality of cooling pipes 22 extending transverselyacross the interior of the furnace at vertical portion at each endextending upward through the furnace Wall to the exterior. One end ofeach of the pipes has free access to the outside air while the otherends of the pipes are connected to a conduit 23 extending lengthwise ofthe furnace. This conduit is also connected to a suitable air blower 24(Fig. 2). Thus by turning on the blower, coolingl air may be forcedthrough the plurality of cooling ducts 22 tof/thereby extract heat fromthe furnace. Itlwill be observed that the pipes "form cooling pathsclosed off from the furnace chamber. The tubes are made of suitable heatresisting material such ,as an alloy of nickel andchromium or an of theurnace at the bottom, each of these.

ducts terminating on the exterior of the furnace in an upwardlyextending ortion 26 which may be closed b a cover 2 Preferably, thecover is seale by providing it with a ange 28 which, when the cover isclosed, enters a suitable liquid 29, such as oil, con` tained in atrough 30 surrounding the upper end of the duct portion 26.

In the roof of the furnace a plurality of vertical ducts 31 areprovided, these ducts being preferably arran ed centrally of the roofand spaced apart romthe front to the back. Each of these ducts isprovided with a sand sealed cover 32 similar in construction to thecover 27.

Preferably the cov'ers 27 and 32 are raised and lowered simultaneouslyto open and close the apertures. As shown, this may be doneI by means ofa. handwheel 33 driving a worm 34 which cooperates with a wormwheel 35.

-Connected to -a crank 36 operated by the wormwheel is a link 37 whichin turn is con-' nected to a crank 38 secured to a shaft 39 mounted onthe furnace and running fromA the front to the back of the furnace. Asimilar shaft 40 is mounted on the opposite side of the furnace andconnected to the shaft 39 through suitable cranks and a link 41 so thatthe two shafts may be rotated together by turning the Wormwheel 35. Eachof the covers 27 is connected to one of these shafts "through s. link 42and a crank 43 connected to the shaft, the covers on a given side of thefurnace being, of course, all connected to the same shaft.

For the operation of the covers 32, a central shaft 45 is provided justabove these covers and extendin from the front to the rear of thefurnace. ach of the covers is secured to a sheave 46 secured in turn tothe shaft 45, the connection between the cover 32 and the sheave beingeffected by a flexible member 47 such as a metallic cable. The shaft 45is connected to the shaft 39 through suitable cranks and a link 48 sothat when the shaft 39 is turned the shaft 45 and with it the sheaves 46are turned to raise or lower l the covers 32. It will thus be observedthat by turning the handwheel 33 all the covers may be simultaneouslyraised and lowered.

In the operation of the furnace after the charge has been suitablyheated the electric current or other source of heat is turned off andthe furnace allowed to cool. For example, in the annealing of a chargeof steel the 3 may be in- 'lhe furnace turned on to force air throughthe cooling tubes l22. Preferably, the diameterof the conduit 23 isgradually decreased, as shown in Fig. 2, from the end connected to theblower to the opposite closed end in order to provide for a uniform airpressure throughout the length of the duct and consequent uniform airflow through the cooling tubes 22.

Aftenthe forced cooling b means of the tubes 22 has been continued fbr atime, such as several hours, sufficient to reduce the charge to apredetermined temperature, such as SOOOFahr., permitting a sheltered exosu're of the charge to the air and at which a igher rate of cooling maybe used without detrimental eifect upon the material, the blower 24 ispreferably shut down althou h it may still be used if desired, and thehan wheel 33 operated to raise the covers 27 and 32 to allow `a naturaldraft circulation of the outside air 'it may be exposed to the outsideair. The

furnace may then be opened and the charge taken out.

It will be observed that we have provided a very flexible' control meansfor the cooling cycle. The natural cooling period and the forced coolingperiod may be varied as desired. Furthermore, where the conditions aresuitable the furnace may be cooled rapidlyimmediately after being shutdown by starting the blower. In the cooling cycle shown by curve A, Fig.3, the natural rate of cooling is continued for about 121/2 hours untilthe material has been cooled down tosomewhat less than l200 after whichthe blower is started and used 'for a period of about 61/2 hours to coolthe material down to somewhat less than 800. The covers 27 and 32 arethen raised to accelerate the cooling rate so that the furnacetemperature after about 5 hours has been reduced to around 400". Thecharge may then be removed from the furnace and further cooled in theoutside air. It will be understood, of course, that this curverepresents the temperatures in the heating chamber of the furnace'andlikewise the temperatures of the outer service portions of the char e.The temperature of the interior of the iarge may be somewhat higherdepending upon its size and the accessibility of its various portions totherfurnace atmosphere.

' In Fig. 3 the lower portion B of the curve indicates a cooling cyclewherein the blower was turned on after about 61/2 hours o f naturalcooling, the blower being used for about the same length oftime to cooldown to about 800 after -which the covers 27 and428 were lifted toaccelerate the cooling. This pro- A vides a shorter cooling cycle. y

What we claim as new and desire to secure by Letters Patent of theUnited States, is: 1. A furnace comprising -walls formin a heatingchamber, cooling ducts extending through at least one of said walls intosaid' chamber giving a predetermined rate of cooling and means providinga limited circulation of air through the furnace to give a higher rateof cooling.

2. A furnace comprising walls forming a heating chamber, heatin meansfor said chamber, aplurality or ducts' extending through said chamber,means for forcing a cooling fluid through said ducts to cool the chamberat a predetermined rate, said walls being provided with apertures inupper and lower -regions for giving a limited circulation of air throughsaid chamberfor amore rapid rate of cooling and closure means for saidapertures.

3. A furnace comprising .walls formingla heating chamber, heating meansfor said chamber, a plurality of ducts extending through said chamber,means for forcing a cooling lluid throu h said ducts, said walls beingprovided with apertures in .upper and walls above said side wallopenings, means for turning said shafts simultaneousl and connectionsbetween said shafts and said closure means. 4

6. The'method of cooling a charge in a furnace provided with closedpathcooling means and also with means providing for limited circulation ofairthrough the furnace which consists in allowing the furnace to cool at.its natural rate down to a predetermined temperature, cooling at agreater rate by said closed pathv cooling means down 'tol a temperaturesuitable to a sheltered exposure to air, then admitting air to provide4for an increased rate of coolingdown to a predetermined temperature an'dthereafter removing the charge from the furnace and allowing it to coolinthe outside air.

7. A furnace comprising walls forming a heating chamber, cooling ductsextendin through at least one of said walls into sai chamber, means for.forcing a cooling iiuid through said ducts to cool the chamber at apredetermined low rate, said walls being provided with Ventilatingapertures for eifecting a circulation of outside air through saidchamber for a higher rate of cooling, and closure means for saidapertures.

In witness whereof we have hereunto set our hands.

CARL L. IPSEN. ALBERT N. OTIS.

4 lower regionsfor giving a limited circula'- v tion of air throu saidchamber, closure means forl said apertures and means for o i y eratinsaid closure means to control t e flow o air through said apertures.

4. A furnace comprising walls forming a heating chamber,4 heating meansfor said chamber, said Wallsbeing provided with a plurality of aperturesin respectively upper and lower regions of said chamber whereby 53 alimited circulation of outside air through said heating chamber may beobtained, a

closure device for each of said apertures and operating means connectedwith said closure l devices for eiecting simultaneous opening or 5iclosincr movement thereof.

5. furnace comprising a plurality of side and roof walls forming aheating chamber, said roof walls being provided with a plunralityofapertures and at least two opposite 5 side walls being providedwith a plurality of apertures communicating with a lower re gion of saidchamber whereby a circulation g of cooling air through said chamber maybe produced, closure mea-ns for said apertures, a 55 shaft mounted oneach of said opposite side

